The present invention relates to flash fusing assemblies which are used to provide a pulse of radiant energy for fusing a toned or printed image on a recording member. In such an assembly, one or more flash tubes located in a reflective housing assembly are fired to create a short duration intense light pulse, and the housing assembly operates to smooth the spatial distribution of the light while redirecting the light such that most light strikes the recorded image.
Such flash fusers offer the primary advantage of requiring power only when they are actively operated to fuse an image, thus eliminating the large power requirements of continuous or semi-continuous standby heaters, hot rolls, and radiant heaters of other constructions. On the other hand, to reap the full benefit of this power savings, the flash power must lie in a narrow power range and be uniformly directed at the image area; it preferably is applied in such a time/dose way as to fuse the toner without transferring excessive energy to the underlying paper sheet or other recording member.
The power-saving ability to operate intermittently is of primary value for low-volume imaging machines, and accordingly there is also a trade-off between the cost of electrical circuit components of sufficient capacity to fire the flash tube at an acceptable power level and flash rate, and the attainable fusing speed in pages per minute. Further, the peak power requirements may be quite large, since the power for each flash is drawn from the power lines immediately before the flash is triggered and there is no inexpensive or easy way to accumulate the energy for multiple flashes at a lower rate of power consumption.
These cost, power draw and efficiency considerations have an especially complex interdependence when it is desired to employ a flash fuser for two-sided copier or to employ multiple overlapping flashes to cover a whole sheet, or when it is desired to produce an efficient fuser which operates both for intermittent and for relatively fast or continuous paper feeds.
To address one or more of these problems, various constructions are known in the art. For example, to direct flash tube light uniformly over an image fusing window it is common to place the flash tube in front of a diffusely reflective curved reflector known as an integrating reflector. The number of reflections of any ray not directly aimed at the toned image is both large and random, so that substantial uniformity of illumination is obtained. It is also known to provide an effective flash combination at relatively slow speed with few circuit elements by providing a single power supply which alternately energizes each of a pair of adjacent flash assemblies, as shown in U.S. Pat. No. 4,386,840. While these steps each contribute to the efficiency of flash design for a particular or limited type of machine, the complicated trade-offs between efficiency, cost, speed and complexity remain, and other improvements are desirable in this area.